Creepiest Thing You've Done

For example:
I think it's pretty strange when two users who don't seem to interact that often, get into a "dispute" of sorts, and one one starts throwing insults based on info they could have only gathered by stalking the other's posting history.
Like, did you really spend ample amounts of time search through the person's profile and years-long posting history for specific information? And archived it?

Whoa.